Air intakes that centrifugally separate heavier-than-air particles from the air to be used in internal combustion engines, ventilation systems, and other apparatus that draw in air laden with debris, are known. The use of in-line filters in air delivery systems to clean the air is also, per se, known. However, air filters are subject to plugging by debris from the air passing through the filter, which eventually increases the restriction to air flow through the filter and decreases the operating performance of an associated device, such as an electronically controlled internal combustion engine being supplied with air through the filter. Frequent filter replacement and shorter service intervals may also be required, which increases the cost of operation. There is a need for an improved air cleaning system and air cleaning method which combine centrifugal separation and air filtration in a manner to efficiently remove debris from debris laden air while reducing or avoiding the aforementioned problems.
A powered air cleaning system according to the invention comprises a flow path extending through the system from an air inlet to a clean air outlet. A motor-driven fan is located along the flow path to draw particulate debris laden air into the inlet and rotate it about an axis to form a rotating flow that stratifies the debris laden air with the heaviest particles in the outermost orbits of the rotating flow. An ejector port is provided for ejecting particulate debris laden air from the stratified rotating flow in the system to the environment. An air filter is located within the rotating flow and across the flow path upstream of the clean air outlet for filtering air from the innermost orbits of the stratified rotating flow. According to the disclosed example embodiments of this invention, the filter is elongated in the direction of the axis about which the debris laden air is rotated. An outer peripheral surface of the filter within the rotating flow is swept by innermost orbits of the stratified rotating flow for minimizing debris buildup on the filter.
An air cleaning method of the invention comprises drawing particulate debris laden air into the air cleaning system with the motor-driven fan located in the system, forming a rotating flow of the debris laden air in the system to stratify the flow with the heaviest particles in the outermost orbits of the rotating flow, flowing air from the innermost orbits of the rotating flow through the filter enroute to the outlet of the system, and returning particulate debris laden air from the stratified rotating flow in the system to the environment. According to the example embodiments air is supplied to a device with a variable air flow demand, which applies a variable vacuum to the outlet of the air cleaning system, and the method further includes operating the motor-driven fan to maintain positive air flow pressure in the system to return particulate debris laden air to the environment from the system at all rates of air flow demand by the device. The positive air flow pressure, acting on the filter of the system located within the rotating flow, keeps debris buildup on the filter to a minimum. Accordingly, the system self-cleans its air filter.
In one example embodiment, the ejector port of the system is located radially outward of the outermost orbits of the rotating flow, in the form of an ejector slot which extends the length of the air filter. This arrangement helps in subjecting the air filter to a slight positive pressure, reducing restriction to the engine or apparatus the air cleaning system is installed on and aiding the self cleaning of the air filter.
These and other features and advantages of the present invention will become more apparent from the following description when taken in connection with the accompanying drawings, which show, for purposes of illustration only, two example embodiments in accordance with the present invention.